U.S. patent number 5,592,540 [Application Number 08/540,365] was granted by the patent office on 1997-01-07 for method and apparatus for selectively delivering telephony signals on a hybrid coaxial cable network.
This patent grant is currently assigned to U S WEST Advanced Technologies, Inc.. Invention is credited to Gregory J. Beveridge.
United States Patent |
5,592,540 |
Beveridge |
January 7, 1997 |
Method and apparatus for selectively delivering telephony signals
on a hybrid coaxial cable network
Abstract
An interdiction device and method to jam or delete selected
video and telephony signals. The interdiction device includes
amplifiers and forward couplers to prevent the telephony signals
from appearing at other undesired subscriber locations on the
network.
Inventors: |
Beveridge; Gregory J.
(Thornton, CO) |
Assignee: |
U S WEST Advanced Technologies,
Inc. (Boulder, CO)
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Family
ID: |
22087596 |
Appl.
No.: |
08/540,365 |
Filed: |
October 6, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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69233 |
May 28, 1993 |
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Current U.S.
Class: |
379/184;
348/E7.075; 379/177; 379/183; 455/26.1; 725/106; 725/129 |
Current CPC
Class: |
H04H
20/79 (20130101); H04H 60/94 (20130101); H04H
60/97 (20130101); H04N 7/17354 (20130101); H04Q
11/02 (20130101) |
Current International
Class: |
H04H
1/02 (20060101); H04Q 11/00 (20060101); H04N
7/173 (20060101); H04Q 11/02 (20060101); H04N
007/10 (); H04N 007/14 (); H04M 013/00 (); H04H
001/00 () |
Field of
Search: |
;379/177,183,184
;348/6-8,12-17 ;455/1,4.2,5.1,26.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0024618 |
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Aug 1980 |
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EP |
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2237709 |
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May 1991 |
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GB |
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2252022 |
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Jul 1992 |
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GB |
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92/10038 |
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Jun 1992 |
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WO |
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Other References
"Using CATV Distribution System for linking POS Telephones" by
Andrew Beasley; Feb. 1992; IEEE pp. 292-295, .
"Integration of Cordless Telephony with CATV Distribution" by
Hardwick et al, 1992, IEEE pp. 87-90. .
European Conf. on Optical Communication; Genoa Italy; 1978 Miki et
al.; two way WDM Transmission. .
Conceptual Design of A Switched Television-Distribution System
Using Optical-Fiber Waveguides; HARA; IEEE Transactions; 1977 pp.
120-130. .
Voice Follows Video; CED: Communications Engineering and Design;
Jun., 1993 p. 67. .
ADC Launches Fiber Coax Platform; Telephony; May 24, 1993; pp.
11-12. .
Omaha Selected For Broadband Roll-out; U S WEST Today; Apr. 26,
1993, vol. 6, No. 7; p. 1. .
Bell's Brash CEO Bets Big on TV Dream; USA Today; Apr. 22, 1993; p.
B 1,2. .
U S WEST Picks Omaha To Test New Data Network; The Denver Post;
Apr. 24, 1993; p. C 1,2. .
Cable Phone.RTM. Telephony For The Cable Industry; Jerrold
Electronics; undated. .
Homeworx Fiber In The Loop System; ADC Telecommunications; Jun.
1992. .
Homeworx Fiber in the Loop System From ADC Telecommunications, A
Partner in the Expanding Network; Mar. 1992. .
Phone, Cable Deals Let U.S. Test Future; USA Today; Jun. 28, 1993,
p. B 1,2. .
ADC Telecommunications Network Configurations; Advertising
Literature; undated. .
Rochester Tel Taps ADC For Video Trial; Telephony; May 31, 1993,
pp. 8-9. .
First Pacific Networks' Wideband Personal Xchange; Telephone News;
Aug. 28, 1989; vol. 10, No. 33. .
Cable, Phone Firms Wrangle Over Future; USA Today; Feb. 11, 1993,
p. B 1, B2..
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Primary Examiner: Chin; Wellington
Assistant Examiner: Shankar; Vijay
Attorney, Agent or Firm: Schulte; Timothy R. Kinsella; Peter
J.
Parent Case Text
This is a continuation of application Ser. No. 08/069,233, filed
May 28, 1993 hereby abandoned.
Claims
What is claimed is:
1. A device for transmission of telephony signals in a downstream
frequency range and an upstream frequency range on a bus based
coaxial cable network including at least a first signal path and a
second signal path to and from a subscriber location
comprising:
an interdiction device connected to said coaxial cable network,
said interdiction device including:
a jamming oscillator connected to said coaxial cable network;
an amplifier connected to said coaxial cable network;
a forward coupler connected to said coaxial cable network; and
a modulator/demodulator connected to said coaxial cable
network;
whereby said interdiction device jams telephony signals in said
downstream frequency range on said second signal path said
amplifier and said forward coupler isolate telephony signals in
said upstream frequency range on said first and second signal paths
and said modulator/demodulator demodulates selected baseband
telephony signals in the downstream frequency range on said first
signal path and modulates baseband telephony signals in the
upstream frequency range on said first signal path such that said
baseband telephony signals to and from said subscriber location may
not be monitored at another subscriber location on said bus based
coaxial cable network.
2. A device for transmission of telephony signals in a downstream
frequency range and an upstream frequency range on a bus based
coaxial cable network including at least a first signal path and a
second signal path to and from a subscriber location
comprising:
an interdiction device connected to said coaxial cable network,
said interdiction device including:
a negative trap connected to said coaxial cable network;
an amplifier effectively connected to said coaxial cable
network;
a forward coupler connected to said coaxial cable network; and
a modulator/demodulator connected to said coaxial cable
network;
whereby said negative trap eliminates telephony signals in said
downstream frequency range on said second signal path, said
amplifier and said forward coupler isolate telephony signals in
said upstream frequency range on said first and second signal paths
and said modulator/demodulator device demodulates baseband
telephony signals in said downstream frequency range on said first
signal path and modulates baseband telephony signals in said
upstream frequency range on said first signal path such that said
baseband telephony signals to an from said subscriber location may
not be monitored at a different subscriber location on said bus
based coaxial cable network.
3. A method for delivering secured telephony service in a bus based
coaxial cable network including at least a first signal path and a
second signal path to and from a subscriber location comprising the
steps of:
demodulating a baseband telephony signal on said first signal path
to said subscriber location in a downstream frequency range;
jamming telephony signals in said downstream frequency range on
said second signal path to said subscriber location;
modulating a telephony signal in an upstream frequency range on
said first signal path from said subscriber location;
isolating telephony signals in said upstream frequency range from
said subscriber location on said first and second signal paths;
and
whereby modulated telephony signals to and from said subscriber
location may not be monitored at another subscriber location on
said bus based coaxial cable network.
4. A method for delivering secured telephony service in a bus based
coaxial cable network including at least a first signal path and a
second signal path to and from a subscriber location comprising the
steps of:
demodulating a baseband telephony signal in a downstream frequency
range on said first signal path to said subscriber location;
eliminating telephony signals in said downstream frequency range on
said second signal path to said subscriber location by reducing the
amplitude of said signals below the noise level;
modulating a telephony signal in an upstream frequency range on
said first signal path from said subscriber location;
isolating telephony signals in said upstream frequency range from
said subscriber location on said first and second signal paths;
and
whereby telephony signals to and from said subscriber location may
not be monitored at another subscriber location on said bus based
coaxial cable network.
Description
FIELD OF THE INVENTION
The invention relates to the field of telecommunications. More
particularly the invention relates to the field of multiplex
communications. In still greater particularity, the invention
relates to the provision of secured telephony in a coaxial cable
network. By way of further characterization, but not by way of
limitation thereto, the invention uses interdiction to prevent
monitoring of a subscriber's telephone communications by another
subscriber on the network.
DESCRIPTION OF THE PRIOR ART
Information, and access to it, has received significant attention
recently. The building of an "information highway" compared to the
national interstate highway system begun in the 1950s has been made
a national priority. There are currently three wireline transport
elements available for such a highway: 1) fiber optic cable;
(2)coaxial cable; and 3) twisted copper pair cable ("twisted
pair"). Presently, twisted pair cable predominates, certainly in
the local loop portion of telephone networks. Coaxial cable has
been used widely by cable television companies and both telephone
companies and cable companies have made use of fiber optics for
main or trunk line signal transport.
Fiber optic cable can carry more information over a greater
distance than coaxial cable, while coaxial cable can carry more
information over a greater distance than twisted pairs. Because
twisted pair is the predominant local loop technology at least in
the telephone industry, attempts have been made to develop
technologies which will increase the carrying capacity of copper.
In reality, copper wire is a very efficient transport means for
traditional telephony services.
Within the telephony industry, the term "broadband" denotes a very
high digital line rate, such as the 156 Megabits per second (Mb/s)
optical line rate of new SONET OC3-level fiber optic systems. The
term "baseband" describes the original (unmodulated) form of the
electrical or optical signal associated with a single service that
is typically presented to the network by a subscriber, and the
final form of that signal presented from the network to a
subscriber. The baseband signal can be either analog or digital in
form, and is further characterized as the direct electromagnetic
representation of the base information to be transmitted, with no
other carrier or subcarrier energy present. A baseband signal may
be carried directly on a transmission line, such as a twisted pair
of insulated copper wires or an optical fiber. A baseband signal
may also be used to modulate a carrier signal for transmission on a
variety of transmission systems (e.g., radio). In
telecommunications, the term "passband" describes the range of
frequency spectrum which can be passed at low transmission loss
through a linear transmission system. Modulated carrier signals
presented to such a system will be delivered in their original form
with minimal loss and distortion, as long as such signals fall
within the absolute limits of the passband range of frequencies and
the dynamic range of signal amplitude for a given linear
transmission system.
An example should help clarify the relationship between baseband
and passband. The electrical signal that is present at a telephone
jack during a conversation is the baseband electrical signal
representation of the talker's voice. This baseband signal is
typically transported to the telephony switching office by a
twisted pair of insulated copper wires. At the central office, the
signal goes through the switch and is typically converted to
digital form and multiplexed in the time domain for transmission
through baseband digital transmission systems that carry such
signals on copper or fiber optic cables to other locations. The
baseband digital transmission system may carry thousands of
individual telephone calls on the same transmission line. Even
though there are multiple calls in progress on the same
transmission line, such a system is still defined as "baseband"
because there is no modulation of a carrier or subcarrier signal
anywhere in the system, and, at any given instant of time, there is
only a single subscriber's signal actually present at a given point
on the line. As the original talker's signal reaches the other
switching office involved on the call, it is convened back to the
original analog form and put on the copper pair connected to the
far-end telephone set, once again in baseband form.
Passband techniques can also be used to provide telephony services.
In cable television systems configured for telephony services, the
baseband analog telephone signal is used to modulate a carrier
signal. The modulated carrier signal can be assigned a particular
frequency within the passband of the linear transmission system. A
number of such modulated carrier signals, each assigned a different
carrier frequency in the passband, can be transmitted all at the
same time without mutual interference. At the far end, a selected
modulated carrier signal must be demodulated to remove the carrier
signal and recover the baseband signal associated with the service.
If the linear transmission system is operating properly, the
derived signal will be delivered to the far-end telephone set, once
again in baseband form.
While there is technology that supports digital line rates on the
order of 100Mb/s for short-distance building twisted-pair wiring,
the practical limit for traditional twisted pair copper plant in
the loop environment (from the serving central office to the
subscriber) is on the order of 1.5Mb/s, at a maximum distance of
about 12 kilofeet (KF). One emerging technology that is capable of
attaining this practical limit for twisted pairs is known as
High-speed Digital Subscriber Line (HDSL). A similar copper-based
technology known as Asymmetric Digital Subscriber Line (ADSL) may
permit the carriage of a 1.5Mb/s downstream signal toward the
subscriber and an upstream channel of perhaps 16 kilobits per
second (Kb/s), all over an existing telephone service on a single
copper pair, within 18KF from the serving central office. Rather
than modify its network to include more fiber and/or coaxial cable,
at least one telephone company is deploying ADSL technology (USA
Today Apr. 29, 1993, Page B1).
While suited for their intended purpose, these emerging
copper-based technologies carry some uncertainties and special
restrictions that may reduce their applicability in copper loop
plant. At this point, the best-case scenario indicates that such
technology could be used only on nonloaded copper loops within 12KF
(HDSL) and 18KF (ADSL), respectively. Thus, this technology would
be employable in substantially less than 100 percent of the present
environment. Other limitations (e.g., within-sheath incompatibility
with other services such as ISDN) will likely further reduce the
maximum penetration percentage.
The maximum practical distance that true Broadband rates (e.g.,
156Mb/s and higher) can be supported on twisted pair copper plant
is on the order of 100 feet. Given that the emerging HDSL and ADSL
copper-based technologies provide line rates two orders of
magnitude below true broadband rates, and then cover substantially
less than 100 percent of the customer base in the best case, copper
is clearly not practical as a true broadband technology
solution.
Baseband signal compression techniques offer possibilities for
leveraging the embedded copper plant for certain specific services.
Baseband compression techniques that compress a standard movie
entertainment television signal with "VCR-quality" into a 1.5Mb/s
channel (including audio) have been demonstrated, as well as
lower-speed devices intended for videoconferencing and
videotelephony applications. The apparent view is that a
bearer-channel technology such as ADSL (described above) and a
baseband compression technology, taken together, could offer a
realistic alternative for video services requiring large bandwidth,
allowing continued use of the existing copper plant and obviating
the need for fiber-based or other broadband links.
Unfortunately, baseband compression techniques use a deliberate
tradeoff of one or more technical parameters that can reasonably be
"sacrificed" as having little or no effect on a given service. For
example, low-bit-rate coders for voice and video obtain bandwidth
efficiencies at the expense of transmission delay. A processing
delay of perhaps a half-second through the encoding and decoding
process will have little or no effect on one-way broadcast service,
but may disturb the natural rhythm of speech in a two-way
videotelephony application, making the two-way service awkward to
use. Baseband compression techniques are narrowly designed for
specific applications (e.g., videotelephony) within generic classes
of service (e.g., video), and do not provide complete transparency
of any baseband digital signal.
Line coding compression techniques that may be used to provide ADSL
capabilities offer bandwidth efficiencies in a variety of ways. In
one category, Quadrature Amplitude Modulation (QAM) techniques have
been used to encode digital information for transmission on
microwave radio systems and (more recently) channel slots on cable
television systems. A 16state QAM coder offers a 4 bits-per-Hertz
(4B/Hz) efficiency; a 64-state QAM coder offers a 6 bits-per-Hertz
(6B/Hz) efficiency. This simply means that an input digital signal
at the rate of 1.5Mb/s can be 16-state QAM-coded into an analog
frequency spectrum of about 0.38 MegaHertz (MHz), making it
possible to be transported on copper wire pairs over longer
distances. Similar techniques are also possible on satellite and
CATV systems, to provide both digital signal carriage and digital
spectrum efficiencies on those media.
In summary, utilizing baseband signal compression techniques
results in bandwidth efficiencies which are gained at the penalty
of one or more technical parameters. Such a tradeoff may not be
possible in the case of a different service on the same medium. In
the case of wireline coding techniques that deal with the signal
after baseband compression, technical complexity and cost generally
limit it to 6/Hz spectrum efficiency. Thus, copper-based systems
such as HDSL and ADSL may find limited application in the telephone
network. HDSL is actually a pure cost-saving loop alternative to
facility arrangements that serve 1.5Mb/s High-Capacity digital
service ("HICAP") customers. The cost savings are potentially
realized by the ability to use assigned nonloaded pairs in the loop
outside plant, rather than designed pairs, as well as going longer
distances without outside plant repeaters.
ADSL technology could provide early market entry for limited
VCR-quality video or other asymmetric 1.5Mb/s applications.
Advantages of ADSL include the use of existing copper plant
facilities and maximization of network functionality. Disadvantages
include the cost of set-top converters which are not reusable after
ADSL is obsoleted. Also, ADSL offers only single channel service.
In addition, the service can only reach a limited number of
customers and telephone service electrical noise can result in
video distortion. ADSL is also subject to RF transmission
interference over longer loops.
Fiber optic-based systems are preferable to copper-based networks
even with HDSL or ADSL because of their high bit rate transport
capability. Information services that require true broadband rates
require fiber or coaxial cable technology, as a practical matter.
Even low-end (i.e., POTS "plain old telephone service") services
will reflect a lower per-subscriber cost on fiber, compared to
present copper-based delivery systems. Specifically, fiber-based
systems that provide residence telephony to groups of 4-8
subscribers with fiber to the curb (FTTC) are expected to achieve
cost parity with copper in the near future. However, the cost to
replace the existing copper plant in the U.S. with fiber optics is
estimated at hundreds of billions of dollars. Thus the length of
time required to achieve this conversion could be decades.
One possible alternative to fiber or copper networks is a hybrid
network which utilizes existing facilities and employs fiber
optics, coaxial cable and copper wiring. Such a network would allow
the delivery of many advanced services and yet be more cost
efficient to allow earlier conversion to a broadband network with
significant fiber optic capability included. At least one company
has announced plans for such a hybrid network (Denver Post, Apr.
23, 1993 Page C1).
In general, hybrid networks combine a telephony network and a video
network. One drawback of such a network is some duplication of
equipment. That is, if, for example, the telephony services could
be provided by sending the telephony signals over the video
network, then a substantial portion of the cost and complexity of
the hybrid network could be eliminated. However, in order to send
telephony and video signals over the same transport medium, the
unique characteristics of each signal must be addressed. For video
signals this is not as difficult as some of the issues surrounding
transport of telephony signals. That is, video signals are
generally sent in one direction, from the provider to the
subscriber, while telephony requires two-way transport. As video
evolves into interactive video, however, two-way video signal
transport issues will also become significant.
Telephony, in addition to requiring two-way communication, has two
other requirements not necessarily addressed by video networks:
powering and privacy of communication. In video networks the power
to operate the subscriber television set, for example, is provided
by the subscriber. That is, the subscriber plugs his or her
television and/or video cassette recorder into an electrical outlet
which provides power in the subscriber location. In the event of a
power outage, for whatever reason, the user is unable to view the
television unless he or she has a backup source of power (i.e.,
battery or generator). Few people have such backup power. In
telephony, on the other hand, subscribers expect phone service
whether or not electricity is available. The following paragraphs
discuss a history of power in the telephony network.
Telephones on the early manual networks had their own battery boxes
which contained dry cells. These batteries were used to power the
carbon granule microphones. In addition, a hand crank generator in
the phone supplied the needed signaling to call others on the same
line, or the operator. These two power sources within the telephone
allowed a user to originate a call and to talk to other users.
Neither of these sources were dependent upon household power,
allowing calls to be placed even before rural electrification.
When automatic switching was introduced into the network, the
battery box was replaced with a common battery located at the
switch, including a common ringing voltage source. The central
office switch also needed power to operate and make connections
between users. Supplying power to each telephone allowed current
flow and the timed interruption of that current (dial pulses) to
signal the switch of the user's intentions. In addition, the busy
state current could be used by the telephone to power the carbon
microphone.
Because of the need to protect the switch and the telephone
connections from service interruptions, the power plant at the
central office was backed up with large wet cell batteries. These
batteries in turn were often backed up with motor-generator sets.
Several different voltages are used within the network, but the
primary supply is -48 volt direct current (vdc) and .+-.105 volts
at 20 Hz.
Over time as the telephone network grew in size and service
penetration approached 100 percent, service availability
(reliability) became one of the most important obligations of the
network. For a time the telephones in users' homes belonged to the
network and were maintained by the network owner. In the past 20
years the ownership of the telephone has changed again and carbon
microphones aren't used anymore. However, the new electronic
telephones with their silicon chips still rely on the network to
supply power for call supervision and even for memory backup.
Service availability is a responsibility shared by the network and
the user. The network is responsible for maintaining the switch and
connecting trunks as well as testing and maintaining the individual
lines to each user. The user also contributes to service
availability by keeping the telephone on-hook when it is not
needed, by maintaining premises wiring and terminal equipment in
good repair, and by limiting the total quantity of equipment
connected to one line.
Maintaining the batteries in the telephone's battery box was
difficult. Thus network power is preferable. First of all, the
financial cost associated with placing the terminal power back in
the terminal equipment would be huge. The supply and maintenance of
the needed batteries would either be forgotten (like those in smoke
detectors) or would be eliminated. Both of these results would
limit the user's service availability. The second reason that power
will likely remain in the network is due to the regulatory bodies
who are concerned with "life-line" services. This relates to phone
service being perceived as a necessity as pointed out above. Basic
telephone service is expected to be available to everyone at a
reasonable cost 24 hours a day.
There are a few exceptions. Some services are powered by the user
today. As more services are introduced in the future, the user
equipment associated with these new services may also be
non-network powered. One good example is Integrated Services
Digital Network (ISDN) services, whether Basic or Primary Rate
Interfaces. With ISDN, the network powers its portion of the
circuit and the user powers the terminal equipment. Most data
services also fall into this category.
Power can only be provided over a fiber optic network with great
difficulty and expense. As discussed above, power can and is easily
provided over a copper-based network. There are video systems today
which utilize cable phone systems in which telephony is provided
over a video network system. However, such systems require power
supplied by the subscriber, usually in the form of AC power and (in
some cases) batteries at the subscriber premises. In addition,
adaptive hardware in the form of converter boxes are needed to
utilize the phone system.
Safeguarding privacy of communications is a fundamental rule in the
telephone industry. This is required by law and violators are
subject to heavy penalties. Telephone subscribers have the
expectation that their usage and their communications will be kept
confidential. The requirement for privacy extends to the identity
of the parties to the communications, and even to the fact that the
communications took place. Traditional loop plant architecture
provides each subscriber a dedicated transmission path all the way
back to the switching central office. Except for the deliberate
case of multiparty service, the physical "star" topology ensures
that every subscriber's communication is not available to others
who are not a party to the communications. Referring to FIG. 1, a
star type network architecture is shown. A star architecture is a
physical point-to-multipoint arrangement. There are two types of
star architectures. In FIG. 1A a private line type of star is
shown. That is each of lines 1, 2, 3, . . . (n) is separate and
distinct and provides a dedicated transmission path to the central
office. In FIG. 1B a party line type of star is shown. In this case
each of the parties commonly connected in this manner may listen to
any of the others. There is no privacy. Such party line
configurations, once common for cost reasons, are gradually being
eliminated as networks are modernized.
Cable television systems are configured in a broadcast bus
architecture, and all services carried on such systems are
inherently available to all subscribers connected to the bus,
including telephone channels carried in the passband. A logical bus
type of architecture is illustrated in FIG. 2A. In a bus
architecture all users share common bandwidth as in a party line
star architecture. Generally, cable companies employ a
"tree-and-branch" style bus architecture (FIG. 2B). This is
essentially a logical bus on a tree and branch physical structure.
Similarly, a party line architecture (FIG. 1B) is essentially a
logical bus on a physical star. In any event, the bus style
architecture used by cable companies, while sufficient for delivery
of video services, does not ensure privacy of communications for
telephony or interactive video services. While encryption
techniques can be used to mitigate the potential problem, they add
cost and are not foolproof. As interactive services that use
voice-response units flourish, more mass-market customers will
routinely be touchtoning such information as credit card numbers
and PIN authorizations. Any bus-based architecture that provides
telephony or interactive video services capability must incorporate
means to ensure privacy of communications.
Finally, it is necessary to provide some means to segregate
services (commonly termed "grooming" in the telephone industry)
provided by the central office into two basic categories: "switched
services" (e.g. POTS) that terminate on the line side of the
central office switching machine; and "special services" (e.g.
burglar alarm, program channel services, etc.) that terminate on
other equipment in the central office. The segregation into these
two categories is accomplished in modern telephone networks by the
use of equipment that provides for Time Slot Interchange (TSI) of
digital signals.
Modern digital switches recognize only signals which are
transmitted in discrete digital rate and format. That is, the
switch views the transmitted/received signal in 64 Kb/s increments.
In order to make the signal intelligible to the switch, it must be
presented in this basic format. For POTS, the switch expects to
"see" a digital signal with a specific line code, line rate, ones
density, frame format, and signaling bit convention, with other
bits used for mu-law voice coding of the talker's voice. Special
services signals are not usually in a form recognizable by the
switch. Conventional networks use pulse code modulation techniques
to convert from analog to digital and vice versa and then use time
division multiplexing to order to sequence (package) a number of
services in a common bit stream for transmission. Time division
multiplexing divides the time during which each message is
transmitted along the data link into discrete time intervals. Each
port on the multiplexer is then sequentially sampled for the time
interval and that data sample is transmitted sequentially or
serially with a number of other data samples from other ports. A
demultiplexer at the receiving end of the transmission then
recombines the serially transmitted data into the port
corresponding to the signal origin. While suited for its intended
purpose, this type of transmission technique requires expensive
time slot interchangers to reorder the time slots to separate
switched services from special services. In addition, the TSI
technique is not transparent to all of the bits. That is, the
ability to perform certain functions such as cyclic redundancy
check code (CRC6) on an end-to-end basis is lost with the TSI
technique.
SUMMARY OF THE INVENTION
The invention is a network for providing video and telephony
services to a subscriber. The network incorporates fiber optic
cable, coaxial cable, and twisted pair copper wiring. The network
provides power for the telephony services from a network location
through coaxial and copper wiring to the subscriber. Power can be
provided over coaxial cable relatively easily. Thus, in the hybrid
network power for the telephony portion of the service is provided
through the network from the point at which coaxial cable and
copper are used. Interdiction devices are used to selectively
transmit video signals to a subscriber location.
The invention relies on the use of fiber/coax passband
infrastructure as the basic bearer channel for all services in the
residential mass market served by the network. The selective
delivering device would be physically located in place of a
curbside Optical Network Unit (ONU), and subsumes all of the basic
telephony functions ("talk" battery, ringing, testing, etc.). The
selective delivery device operates as the source/sink element for
baseband telephony, is powered over the coaxial cable plant from
the optical node typically serving up to 400 subscribers, and
provides complete transparency for the entire two-way passband
spectrum into 4-8 homes, except for the channel slots used to
transport telephony services. In one embodiment the actual link to
the home consists of a twin-coaxial-cable "drop" that derives the
tip/ring RJ-11 interface from the center conductors of the coaxial
cable pair at a Network Interface (NI), compatible with all
existing inside telephony wire arrangements. The other output of
the NI is a standard F-fitting CATV connector, compatible with the
existing coaxial cable inside wire. The curbside device also houses
the passband interdiction device. In the preferred embodiment, the
NI at the residence includes only passive filters and no active
electronics.
The invention addresses the issue of communications privacy by
permanently interdicting all of the telephony channels in the
passband for both directions of transmission. The interdiction is
accomplished external to the premises of all subscribers so served.
No modulated telephony signal ever appears in recoverable form on
the coaxial cable drop, ensuring complete privacy of
communications. This can be accomplished by several means. One
method involves the permanent insertion of a truly random jamming
signal in the pan of the passband that contains the telephony
passband channels in the direction of transmission toward the
customer. An alternative method involves the use of a negative trap
(e.g. band-stop filters) that prevents any of the telephony
passband channels from reaching the drop cable toward the
subscriber. In the set of passband frequencies for the upstream
direction of transmission (toward the central office), an isolation
amplifier and suitable directional coupler arrangement prevents any
individual subscriber from monitoring the upstream telephony
channels of other telephony subscribers on the bus. Conventional
jamming or negative trap techniques in the upstream direction of
transmission are not appropriate, since there are other
applications that originate from the subscriber premises that use a
portion of the upstream frequencies. This requires transmission
transparency from the subscriber toward the network. A preferred
embodiment of the invention uses a modified interdiction device
external to subscribers' premises to accomplish this function.
Nonswitched telephony special services (burglar alarms, etc.) must
be sorted from ordinary switched telephony services. In the
preferred embodiment, the present invention performs this function
by frequency assignment at the remote telephony channel modulators
and demodulators. This is accomplished by remotely setting both
transmit and receive frequencies of the individual channels from
the central office. At the central office, the blocks of switched
services of modulated telephony channels in the passband are
converted to/from the framed digital format required by the
telephone switch, and the blocks of nonswitched special services
are converted to the framed digital format and bypass the switch,
or are further transported to other locations. Thus, use of the
Time Slot Interchange (TSI) technique with its assorted limitations
and high cost equipment is eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates a "star" type network architecture with a
private line architecture;
FIG. 1B illustrates a "star" type network architecture with a party
line architecture;
FIG. 2A illustrates a "bus" type architecture with a traditional
bus;
FIG. 2B illustrates a "bus" type architecture with a cable type
bus.
FIG. 3 illustrates a broadband hybrid fiber/coaxial cable network
architecture;
FIG. 4 illustrates an alternate hybrid fiber/coaxial cable network
architecture;
FIG. 5 illustrates a preferred embodiment of the invention for a
hybrid fiber/coaxial cable network architecture;
FIG. 6 is a schematic illustrating a baseband below passband curb
unit;
FIG. 7 is a schematic illustrating the interdiction device to
ensure privacy protection for the preferred embodiment;
FIG. 8 is a schematic illustrating a network interface for the
preferred embodiment; and
FIG. 9 is a more detailed drawing illustrating the combiner and
splitter unit; and
FIG. 10 illustrates network line cards.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Like reference numerals will denote like structure throughout the
description of the various figures. Referring to FIG. 3, a
broadband hybrid fiber/coaxial cable network architecture is shown.
A digital switch 11 and a video transmission device 12 including RF
modulators 9 and electric/optical converters 10) are shown in a
central office 13. Digital telephony signals are carried over DS1
lines 6 through SONET multiplexer 19 to a fiber optic cable 14.
This architecture represents a fiber to the curb (FTTC) type of
architecture with a video remote transport overlay. That is, fiber
optic cables 14 carry digital telephony signals (SONET OC3) from
the central office through a remote digital terminal 18 to an
optical network unit 15 (ONU). ONU 15 may include a video
interdiction device 16 or interdiction device 16 could be
separately located as shown in FIG. 3. The analog video signals
(AM-FDM) are carried through fiber optic cable 14 to one or more
remote nodes which may include an analog passband video receiver 17
which includes optical/electrical converters where the analog optic
signals are converted to analog electrical signals on a coaxial
cable 24. A power supply cable 20 which may be a 22 gauge
electrical cable supplies power directly from power source 32 in
central office 13 to optical network unit 15. From optical network
unit 15 telephony services may be provided to subscriber premises
21 over a conventional twisted copper pair line 22 to a telephone
27. Typically an ONU serves up to eight subscriber locations. Video
services from a number of video information providers 23, such as
satellite systems or video storage/retrieval equipment, or other
suppliers provided to subscriber premises 21 through coaxial cable
24. A video set-top converter 25 may or may not be required to
descramble these video signals to a television 26.
The network depicted in FIG. 3 solves several problems associated
with the delivery of telephony and video signals to the home. That
is, since the signals are carried on separate transport systems,
each of the signals may be treated separately. For example,
telephone 27 in subscriber premises 21 may be powered from central
office 13 as is done in conventional telephony. Powering of the ONU
may be done from the video network. Powering of the set-top
converter 25 and television 26 may be done from subscriber premises
21. In addition, privacy issues with respect to telephony services
over copper wire 22 are maintained as in a conventional telephony
network. As is known in the art, more than one ONU could be
connected to terminal 18. Similarly, more than one interdiction tap
16 could be connected to receiver 17. The drawbacks with the
network shown in FIG. 3 include complexity and cost. That is, fiber
optic cable 14, power cable 20, and coaxial cable 24 must be laid
from each central office 13 to each optical network unit 15 or
subscriber premises 21. In addition, additional equipment such as
remote digital terminals 18 are required to efficiently transport
the optical signals.
Referring to FIG. 4, an alternate hybrid fiber coax network is
illustrated. As with FIG. 3, central office 13 includes telephone
switch I 1 and video transmission equipment 12 from which a system
manager 28 controls various ancillary functions of video services
supplied from providers 23. As with the architecture in FIG. 3,
telephony signals and video signals are carried from central office
13 on fiber optic cable 14 through the feeder portion of the
outside plant 29. The telephony signals are passed through remote
digital terminals 18 and supplied through fiber optic cable 14 to
optical network unit 15. The video signals are transported to video
receiver 17 where they are converted from optical to electrical
signals on coaxial cable 24. The video signals are then supplied to
interdiction device 16 at the location of the optical network unit
15. In this embodiment ONU 15 and interdiction device 16 are
preferably co-located. The major difference between FIG. 4 and FIG.
3 is that power may be supplied through coaxial cable 24 by a power
supply 32 which may include an electrical connection to the
electrical utility and backup batteries. Thus, power supply cable
20 in FIG. 3 is eliminated.
The elimination of power supply cable 20 represents a significant
cost savings over the architecture of FIG. 3. As with FIG. 3, the
video signals through coaxial cable 24 are supplied to customer
premises 21 through interdiction unit 16 contained in optical
network unit 15. Power is now supplied to telephone 27 from power
supply 32 through coaxial cable 24. Coaxial cable 24 from optical
network unit 15 to customer premises 21 supplies only video signals
to television 26 and does not supply power. As with FIG. 3, a video
set-top converter 25 may or may not be included in the system. FIG.
4 represents a substantial improvement over the network shown in
FIG. 3 in that the elimination of power supply cable 20 results in
significant cost savings and simplifies the architecture.
While the architecture of FIG. 4 is an improvement on that of FIG.
3, it would be even more significant if the telephony signals and
the video signals could be carried on a common transport system,
thus eliminating the duplication of fiber optic cables shown in
both FIG. 3 and FIG. 4. By carrying the video and telephony signals
over a common integral network transmission system, however, other
issues are raised. Chief among these issues is a privacy issue.
That is, if the telephony and video signals were both sent to the
subscriber premises 21 over the same line in the example, it may be
possible for a subscriber to "tap" into the telephony signals of
all neighbors connected to the coaxial cable bus. This would be
done by tuning and demodulating from the myriad of carrier channels
on the coaxial cable in the telephony signal range. It would be
relatively easy for one minimally skilled in electronics to devise
means which could "tune in" on these telephony channels carried in
the spectrum. This is possible because the other telephony signals
in the example also emanate from the remote optical node 17. With
one coaxial cable system carrying all of these signals a subscriber
is able to access the signals of these other subscribers.
Referring to FIG. 5, the preferred embodiment of a fiber/coax
transport architecture is shown in which the telephony and video
signals are transported through a common integral network. That is,
central office 13 includes telephony switch 11 and video
transmission equipment 12 as shown in FIGS. 3 and 4. Alternative
video suppliers 23 could supply video signals to video transmission
equipment 12. Telephony signals from switch 11 and from special
services equipment 33 are supplied to a digital conversion RF
modulator/demodulator unit 34. The telephony signals must be
modulated to be transported on the analog passband fiber optic
cable 14. The video signals from video transmission equipment 12
are combined with the telephony signals in a combiner transceiver
unit 35. These optical signals are sent (and received) on fiber
optic cable 14 to/from an optical node 17 which includes an
optical/electrical conversion unit as shown in FIGS. 3 and 4. The
remote digital terminal 18 as shown in FIG. 4 is eliminated because
the distribution function it performs is no longer needed. Power
plant 32 is co-located with optical node 17. By elimination of
remote digital terminal 18 and the associated fibers in the main
fiber optic cable, significant cost savings are achieved by this
architecture over that shown in FIG. 4. However, it is the
elimination of remote digital terminal 18 on the ONU 15 which
raises the privacy issue. The combined telephony and video signals
from optical node 17 along with the power supply from power plant
32 are carried on coaxial cable 24 to a selective delivery means
which may include a Baseband Below Passband (BBP) device 37. Device
37 includes many of the functions performed by optical network unit
15 in FIGS. 3 and 4 with significant additions and modifications.
Telephony and video signals are supplied to telephone 27 and
television 26 on subscriber premises 21 through a network interface
43.
Referring to FIG. 7, BBP unit 37 is shown in greater detail. BBP
device 37 includes an interdiction device 16 also used for
telephony, a modulator/demodulator unit 39, and a power converter
unit 41. Interdiction device 16 is a modification of the standard
interdiction device known in the art and used in video networks.
That is, a device such as an eight-port interdiction unit available
from Scientific Atlanta Corporation (Model No. 9508-021) may be so
modified. The standard interdiction device uses a jamming
oscillator 49 to jam certain channels and transmit only those which
are made available to the subscriber. Alternatively, a negative
trap (consisting of band-stop filters) could be used in place of
oscillator 49 as an interdiction device to attenuate the
nondelivered channels below the noise floor. Interdiction device 16
is modified in the preferred embodiment by including isolation
amplifiers 47 and forward coupler 48 in the upstream direction of
transmission such that only the baseband telephony signal to and
from the subscriber to be served is available at a given subscriber
location. That is, the standard interdiction device is modified so
that all of the downstream telephony channels are interdicted and
each upstream 5-30 MHz port is isolated. Thus, a subscriber is
prevented from tuning into telephone calls of other subscribers on
the network.
Referring to FIGS. 5 and 7, a schematic of the privacy protection
afforded by the present invention is illustrated. Central office 13
sends video and telephony signals "downstream" to subscriber's
premises 21 and receives signals associated with video, and
telephony signals sent upstream from subscriber's premises 21. The
architecture is essentially a "bus" type architecture (see FIG. 2).
Thus, absent any precautions, each subscriber could monitor the
video and/or telephony signals from other subscribers on the bus.
For downstream video this is not a problem. The cable television
company today uses this type of system and the only concern is to
interdict (jam or trap) selected premium channels which the
subscriber has not paid for. However, if interactive video and/or
telephony are added, privacy becomes important.
In order to ensure privacy in this type of network, in addition to
interdiction device 16, and modulator/demodulator device 39,
additional protection is needed. Unless modified, interdiction
device 16 ensures that only selected downstream video channels are
delivered to subscriber premises 21. Modulator/demodulator device
39 ensures that only selected telephony channels are delivered to
and from subscriber premises over the telephone line. However, for
interactive video and to prevent the selective tuning to other
subscribers telephone channels through the interactive video line
24 connected to F-fitting connector 46, additional interdiction is
needed. In the preferred embodiment, isolation amplifier 47 and
forward coupler 48 are added to a modified jamming oscillator 49 in
interdiction device 16.
Amplifier 47 and coupler 48 may optionally be combined with
bandpass filters (not shown) as is known in the art to selectively
transmit a subset of upstream signals. As discussed above the 5-30
MHz bandwidth is used for telephone and interactive signals
associated with video communications. There are three usable 6 MHz
channels in this bandwidth from approximately 8-26 MHz. Since each
6 MHz channel can carry over 400 individual telephony channels,
only two channels would generally be needed for telephony in the
preferred embodiment. The other 6 MHz channel is available for
interactive control/request signals associated with video services.
Amp 47 and coupler 48 (optionally with selective filters)
selectively transmit only the interactive signals associated with
video channels in the upstream direction. All of the channels used
for telephony are eliminated in the downstream direction by
interdiction device 16. Thus, there is no way for any particular
subscriber to listen to the telephony channels of another
subscriber in either direction of transmission. Privacy is thus
assured.
Referring to FIG. 6, modulator/demodulator device 39, which may be
a cable telephony device such as "CablePhone.RTM." which is
commercially available from Jerrold, Inc., demodulates the
telephony signal from coaxial cable 24 and may send the demodulated
telephony signal through standard copper tip and ring wires 42
directly to telephone 27. Modulator/demodulator unit 39 also
receives the baseband telephony signals from telephone 27 in
subscriber premises 21 and modulates that signal onto coaxial cable
24. Optionally, modulator/demodulator unit 39 could send the
baseband telephony signal to combiner 44 to be combined with
passband signals such as video onto coaxial cable 24. BBP device 37
also includes a power converter 41 which supplies -48 volt DC
power, .+-.105 volt AC ringing power, and other converted power for
the modulator/demodulator unit 39 to power the telephone 27 as in a
standard telephony network.
Referring to FIGS. 5, 6 and 7, telephone 27 and television 26 on
subscriber premises 21 receive the video and telephony signals
through a network interface 43. In the embodiment shown in FIG. 5,
the video signals from interdiction device 16 and the telephony
signals from modulator/demodulator device 39 are combined in a
combiner unit 44 (FIG. 6) and then sent over dual coaxial cable
drops to a splitter. Referring to FIG. 8, splitter 36, 38 is
contained in the network interface unit 43 shown in FIG. 5. That
is, passive electronics are also included in network interface 43.
The network interface unit 43 includes a high pass filter 36 with
DC blocking to provide RF transparency for all passband frequencies
and to block all telephony signals. A low pass filter 38 with DC
transparency removes RF passband energy and passes all telephony
signals. A twin carbon block protector unit 50 is also included as
is known in the art. A standard RJ-11 telephony connector 45, and
an F-fitting connector 46 which is standard in the video cable TV
network are included. Because the connectors are standard, the
subscriber premises would not have to be rewired or locally powered
to deliver services from this network. While the embodiment shown
is the preferred embodiment, it is also possible to connect the
coaxial cable from modified interdiction device 16 directly to the
network interface F-fitting 46 and the copper wire 42 from
modulator/demodulator device 39 directly to the RJ-11 connector on
network interface 43. In either event, the modulated telephony
signals which would otherwise be carried onto coaxial cable 24
along with the video signals are eliminated at interdiction device
16 such that only the demodulated telephony signal from demodulator
device 39 is available to a particular subscriber. Thus, any
possibility of a subscriber eavesdropping on telephone calls from
other subscribers is eliminated. If more than one coaxial cable
bearing video services is supplied to network interface 43, a
P-Intrinsic-Negative (PIN) diode switch or other devices known in
the art, for example, could be used to allow the subscriber to
select which set of services he or she would prefer at any
particular time.
The BBP unit 37 enables the network architecture shown in FIG. 5 to
provide the best features of the two basic wire line approaches to
residential access architecture (baseband FTTC and passband cable
television) and solves for the respective problems of each approach
at a cost significantly less than utilizing both types of network
as shown in FIGS. 3 and 4. The network architecture disclosed in
FIG. 5 provides a true broadband network that subsumes all existing
services and all future services for telephony and video services
at a cost substantially less than other types of hybrid
networks.
Referring to FIG. 9, a more detailed description of the combiner 44
and splitter 36, 38 is shown. As previously described, combiner 44
is contained in BBP unit 37. Combiner 44 preferably includes
commercially available L-Section filters 52 shown schematically.
These filters are contained in RF-shielded enclosures 53 providing
greater than 65 Db of isolation over the passband between each of
coaxial cables 24. The splitter includes commercially available
high pass filters 36 and low-pass filters 38 contained in network
interface 43. As with the combiner, the filters are contained in
RF-shielded enclosures 53 providing more than 65 dB of isolation
over the passband between coax cables 24 which are connected to
F-fitting 46.
The present invention uses frequency division rather than Time Slot
Interchange (TSI) techniques to map the signals for transmission.
By so doing, the cost associated with TSI equipment and the
nonenablement of certain functions such as monitoring signal
degradation (CRC6) is removed. Although TSI could be employed in
the network of the present invention, frequency assignment
techniques are preferred because the signals are already in the
frequency domain for transmission. The present invention uses a
linear channel which simultaneously transmits the signals parallel
in time rather than in series in time. There is no mutual
interference among the signals in the linear channel because they
are transmitted at different frequencies.
Referring to FIG. 10, frequency division signal transmission is
accomplished by remotely setting the specific transmit and receive
frequency pairs for each channel card 51 in BBP device 37. Thus,
segregation of switched services and aggregation of special
services into contiguous spectrum is accomplished at the location
nearest the user of the services. At central office 13 the RF
modulated channels are convened to/from 64 kilobit per second
(64Kb/s) channels that are grouped together in blocks of 24, then
formatted into a standard framed DS1 signal for termination on the
digital switch 11. DS1 signals composed of only special services
are routed to other terminal equipment, or transmission equipment
for carriage to other locations. This approach allows the bulk
conversion of groups of modulated carrier signals to/from DS1
digital signals, obviating the need for either Time Slot
Interchange or individual carrier frequency translation ahead of
bulk A/D conversion at central office 13. Another advantage of the
approach is having "universal" channel cards 51 within a given type
of service that can be installed in any slot in any BBP device 37.
Thus, spare/replacement inventories of each are kept to a minimum.
The frequency pairs associated with each card are set and
controlled remotely, preferably in central office 13, such that the
users may not alter the cards.
Each subscriber is assigned a unique transmit and receive frequency
pair for telephony and special services. The assigned frequency
pair is controlled from central office 13. Thus contiguous
frequency assignment to card 51 in BBP device 37 is achieved. This
permits grouping of nonswitched special services that will not
terminate on the digital switch. Time slot interchange segregation
of special and telephony services at central office 13 is
eliminated. Since an optical node 19 could serve as many as 50 BBP
curb devices 37, the frequency division technique allows for
assignment of any available frequency pair to any service channel
card 51 at the BBP device 37, regardless of physical location of
the BBP device 37.
There are several significant benefits of the new BBP element. The
first is the elimination of the baseband fiber-to-the-curb (FTTC)
portion of previously known hybrid networks. This is made possible
by the incorporation of the telephony services in the passband
portion of the network, greatly simplifying the overall complexity
of the outside plant portion of the architecture. The telephony
services are provided by a cable telephony method which employs
signal modulation with some important differences. Since talk
battery and ringing voltage are powered from the network, local
(inside home) powering problems are eliminated. Since the passband
frequencies that carry telephony services are blocked beyond the
selective delivery device, it is not possible to monitor other
telephone subscribers' communications from a given residence. Thus,
the privacy issues associated with telephony services previously
provided through hybrid video-type networks are eliminated.
While the invention has been disclosed with respect to a preferred
embodiment, changes and modifications may be made which are within
the intended scope of the invention as defined by the appended
claims.
* * * * *